Marine Pest Species at Sandspit, Northern New Zealand

The invasive Asian paddle crab Charybdis japonica brandishes its nippers in a defiant stance in front of the Sandspit Yacht Club. This aggressive crab has the potential to alter the ecology of natural shallow reefs in sheltered areas by competing with native species and changing the trophic balance. It is now established at Auckland, Sandspit, Mahurangi and Whangarei harbours.

1. Summary

Six species of marine invasive invertebrates are recorded from the Sandspit Estuary. At least two have the potential to become a nuisance either within the estuary or if they are spread to areas outside the estuary. One (Styela clava, the clubbed tunicate) is a new record for the Sandspit estuary. It is on the Biosecurity NZ list of “unwanted organisms”, and it is illegal to knowingly transport this species to other marine areas without specific approval. Another (Eudistoma elongatum, the Australian droplet tunicate) is so abundant and unsightly at Sandspit as to constitute a nuisance or risk species. Sandspit is presently the southernmost known location for this sea squirt which is found in some Northland estuaries. The biosecurity risk implications for the Sandspit Yacht Club Marina Society plans for dredging a new marina in the estuary are discussed.

2. Introduction

Marine pests are species that are not indigenous to New Zealand, but which have been introduced to our waters by human activities and have the potential to cause significant impacts on our marine environments and resources (Marine Biosecurity Porthole, MPI 2012). Many hundreds of marine species have been introduced to New Zealand, most via shipping, but many have either died out as conditions here were unsuitable for their establishment, or have survived but have no particular harmful impact. A few, such as the Pacific oyster Crassostrea gigas, have become valued as seafood items and are important in aquaculture.

There are, however, some species that can smother, compete with or displace indigenous species, alter coastal habitats, affect human health and damage our fishing or aquaculture, or are simply offensive and unsightly in coastal environments.

As a small island nation a long way from the rest of the world, New Zealand is heavily dependent on shipping trade and is vulnerable to harmful marine organisms that are introduced either attached to ships hulls or via ballast water, imported floating drilling rigs, or slow yachts from overseas. This is an ongoing problem as shipping networks expand and marine pests have more opportunity to reach New Zealand.

Once marine pests get here, usually through major ports where ships from overseas discharge or load cargo, there is then the potential for species to be spread to other parts of the coast through local commercial shipping, movement of aquaculture equipment, disposal of dredged material, and movement of private boats and yachts. Protocols and some laws are in place to minimize this problem, such as by requiring hulls to be cleaned and antifouled from time to time, and aquaculture equipment to be sterilized before being moved to other marine areas. We all have a moral responsibility to minimize the further spread of any marine pest species, just as we are diligent to avoid spread of rats and other pests to our precious offshore islands.

At Sandspit on the east coast north of Auckland, observations over many years, and a very recent survey specifically looking for pest species, have noted six non-indigenous marine species within the Sandspit estuary. While some of these are of little concern, at least two species are of serious concern and need further consideration particularly in view of the proposed dredging of a marina basin in the area where these species have been found. Disposal of dredged material could become a significant vector in the undesirable spread of these unwanted or nuisance marine pest species.

A targeted Government-supported surveillance programme for non-indigenous marine species focuses surveillance activities at major ports and associated marinas around the country (not including Sandspit). This is designed to detect the presence of non-indigenous and potentially invasive marine flora and fauna identified as presenting a significant risk of arriving and establishing in New Zealand, and monitors changes in distribution of established pest species at these locations (Acosta et.al. 2012). Three of their four secondary target species (Musculista senhousia, Styela clava and Eudistoma elongatum) have been found at Sandspit during this survey.

4. Observations and recent surveys

General observations over many years have noted the presence of widespread non-indigenous species such as the Pacific oyster. It has been in northern New Zealand since the early 1970’s and has been widespread throughout the Sandspit estuary for many years. Other species have been noted more recently, such as the Australian droplet tunicate which was first observed in the Sandspit estuary in 2010 and has become abundant through much of the estuary since then, including seasonally on the piles of the Sandspit jetty. Occasional shells of the Asian date mussel have been seen in the estuary for several years, but specifically noted on 3 January 2014. The Asian paddle crab was found at low tide in the proposed marina footprint on 29 March 2013. The most recently noted marine invasive species is the clubbed tunicate, first seen on the Rainbow’s End side of the estuary at low tide on 3 January 2014.

Specifically within the foot print of the proposed marina, low tide observations on 6 January 2014 found abundant Australian droplet tunicate along the low tide fringe. Then on 16 January 2014, snorkeling observations confirmed abundant Australian droplet tunicate throughout the channel within the proposed marina footprint and past the Sandspit Yacht Club at least as far as Lee’s jetty. At the same time the Asian paddle crab, the parchment worm and the clubbed ascidian were observed in the small boat basin immediately in front of the Sandspit Yacht Club.

Details of these observations are included in Table 1, with some locations mapped in Figure 1.

TABLE 1. Occurrence of non-indigenous marine species at Sandspit

Common name

Species

Biosecurity concern

Date

Location

Abundance

Notes

Lat. 36°S

Long.174°E

Parchment worm

Chaetopterus sp.

low

2.5.13

23.828′

44.526′

few

Seen in underwater photo amongst boulders in channel

16.1.14

23.489′

43.555′

few

In basin in front of Sandspit Yacht Club

Asian date mussel

Musculista senhousia

low

3.1.14

23.150′

43.710′

1 dead shell

Probably present in Sandspit estuary for many years

Pacific oyster

Crassostrea gigas

low

Since 1970’s

widespread

abundant

On intertidal rocks, man-made structures and mangroves

Asian paddle crab

Charybdis japonica

moderate

29.3.13

23.434′

43.568′

1

Fell into sediment trap

16.1.14

23.489′

43.555′

4

In yacht club basin

Clubbed tunicate

Styela clava

high

3.1.14

23.150′

43.710′

4

Attached to shells and pebbles at low tide

16.1.14

23.489′

43.555′

1

In yacht club basin

16.1.14

23.487′

43.548′

1

In yacht club basin

Australian droplet tunicate

Eudistoma elongatum

high

31.10.10

Edge of entrance channel

common

On shells near low tide (Frances Hall pers.comm.)

10.1.11

23.328′

43.809′

abundant

On wharf piles at Sandspit wharf

2.5.13

23.828′

44.526′

common

Small individuals in remote underwater photo

2.5.13

23.554′

44.145′

few

Dredge sample on shelly fine sand in channel

3.1.14

23.150′

43.710′

abundant

Rainbow’s End lower intertidal

6.1.14

23.392′

43.605′

abundant

Lower intertidal at N end of marina footprint

6.1.14

23.463′

43.533′

abundant

Lower intertidal at S end marina footprint by red buoy

16.1.14

23.380′

43.600′

abundant

Shallow subtidal on sandstone N end marina footprint

16.1.14

23.480′

43.470′

abundant

Off Lee’s jetty, SW end of marina footprint

16.1.14

23.498′

43.558′

common

On wharf piles at Sandspit yacht club

Figure 1

5. Discussion of each non-indigenous species

5.1. Parchment worm (Chaetopterus sp.).

There is still some doubt over whether the parchment worm is indeed an overseas invasive species. It had been found on one occasion in northern NZ in the late 1960’s or 70’s, but was not seen again until the mid 1990’s when it suddenly became super-abundant in the Hauraki Gulf, occupying rock crevices and carpeting large areas of sheltered sediment seafloor (Acosta & Tricklebank 2002). This was much to the detriment of crevice-dwelling reef fauna and soft-sediment benthic animals and scallops. The paper-like tubes washed up on beaches in deep drifts. After several years its abundance reduced, and now it appears to have assimilated into the ecology of our shallow seas and rarely becomes abundant. This “boom and bust” behaviour is common with invasive marine species, suggesting the parchment worm is most likely an import. Because of its rather strange internal structure its true identity is very difficult to determine even for experts in the field.

At Sandspit I have observed it in remote underwater photos in the main entrance channel amongst boulders, and more recently in the boat basin immediately in front of the Sandspit Yacht Club (Figure 2). The parchment worm is not currently a biosecurity concern.

5.2. Asian date mussel (Musculista senhousia).

The Asian date mussel (Figure 3) arrived in Auckland in the mid 1970’s. It formed solid carpets in muddy harbour intertidal areas (Morley 1988) and off shallow fine sand beaches like Cheltenham, smothering the natural marine life. It spread rapidly to many other northern areas and has probably been at Sandspit for many years. Like some other invasive species it went through a “boom and bust” phase and is now likely to be present at only low density at Sandspit, represented by the single dead shell I found at low tide on the Rainbow’s End side opposite the wharf on 3 January 2014.

The Asian date mussel is not currently a biosecurity concern.

5.3. Pacific oyster (Crassostrea gigas).

The Pacific oyster arrived in New Zealand in the early 1970’s and was initially scorned by commercial oyster farmers because its shell was not sufficiently robust to cope with the rough handling treatment they gave the native rock oyster they were farming at the time. With a change in methods, the faster growth ensured it became the species of choice. They have largely replaced the native rock oyster on many shores. They have been abundant in the Sandspit area for many years on natural hard shores, mangrove roots and trunks, and man-made structures (Figure 4).

The Pacific oyster is not currently a biosecurity concern.

Figure 2. The parchment worm is widespread in low numbers in the Sandspit estuary, here photographed in the small boat basin in front of the Yacht Club.

Figure 3. The Asian date mussel is now likely to be present at only low density at Sandspit. This photo shows a live specimen with its foot extended.

5.4. Asian paddle crab (Charybdis japonica).

The Asian paddle crab first appeared in Auckland in 2000. It is a much more aggressive crab than the native paddle crab common off sandy beaches. It has spread northwards and is now found in the Mahurangi Harbour and Whangarei Harbour. The Asian paddle crab may compete with other native crabs and could have an influence on the ecology of shallow water areas in harbours and moderate shelter. At Sandspit I have so far seen five of these crabs of medium size, all within the proposed marina footprint (Figure 5 and cover photo).

Although the Asian paddle crab has no particular biosecurity status, I believe it is of moderate biosecurity concern.

Here’s a video of the invasive Asian paddle crab right in front of the Sandspit Yacht Club. This is a VERY stroppy crab and could rival the native paddle crab as a toe-biter. This, too, would likely be spread to areas it is not presently found if they dump marina dredgings at sea.

5.5. Clubbed tunicate (Styela clava).

Native to the northwest Pacific, the clubbed tunicate was first found in Auckland in 2002 (Hayward and Morley, 2009) and has spread fairly widely to ports in Northland and several other ports since then at least as far as Lyttelton. It is a solitary sea squirt, that is each is an individual animal which attaches to hard surfaces with a stalk, but it can develop to form substantial clumps of many individuals. It is usually found in new areas attached to man-made structures such as wharf piles and mooring lines, but quickly spreads to natural rock surfaces, and can attach to shells and pebbles on otherwise soft seabed. It can compete with native fauna and is regarded as a serious risk to aquaculture. I have recently found the clubbed tunicate in the Sandspit estuary, (a new record for Sandspit), at low tide on the Rainbow’s End side opposite the Sandspit jetty (four specimens)(Figure 6), and more recently subtidally in the small boat basin immediately in front of the Sandspit Yacht Club (two specimens)(Figure 7) within the proposed marina footprint.

Because of overseas experience with this invasive species, soon after its discovery in New Zealand it was classified as an “unwanted organism”, which gives it a clear legal status and it is illegal to knowingly move or spread this animal to other marine areas without specific permission from the relevant authority. Although now widespread in the Hauraki Gulf, according to distribution maps on the Biosecurity NZ website it is not yet found at Great Barrier Island or on the Coromandel east coast.

Because the clubbed tunicate has a very short natural dispersal phase (24- hour life time for planktonic eggs and larvae), its ability to spread naturally is very limited and its main means of distribution is through physical movement of adults by human intervention.

The clubbed tunicate is a serious biosecurity concern and the only non-indigenous marine species at Sandspit with a legal status (unwanted organism) reflecting that concern.

Figure 4. The Pacific oyster has been in Sandspit estuary since the mid 1970’s, here photographed on the rock embankment by the Yacht Club.

Figure 5. The Asian paddle crab is very aggressive and will likely compete with native marine life, potentially altering shallow rocky reef ecology. They would also be serious toe-biters for swimmers! Seen here by the Yacht Club.

Figure 6. The clubbed tunicate was first found in Sandspit at low tide off Rainbow’s End, attached to shells and small pebbles on the channel edge.

Figure 7. Here seen in the basin in front of the Yacht Club, the clubbed tunicate has a legal status of “unwanted organism” and may not knowingly be moved to other marine areas without specific approval from authorities.

5.6. Australian droplet tunicate (Eudistoma elongatum).

This ascidian is colonial. Each apparent “individual” is in fact a colony of hundreds of tiny animals working together to form the structure we see. It first appeared on an oyster farm in Houhora, Northland, in 2005, and then at Parengarenga and Bay of Islands also on oyster farms (Smith et.al., 2007).

It was first noticed in Sandspit in 2010 (Frances Hall, pers.comm.), and has spread through the channels and lower intertidal, becoming particularly abundant in summer. It is locally known as “sea snot”, which, to those who know it, is an entirely appropriate colloquial name. It forms cream/white flaccid colonies about 20mm in diameter and commonly 20 to 30 cm long, although it can grow much larger. It is found toward low tide attached to shells and rocks along the channel margins, and is abundant in subtidal parts of the estuary including the Sandspit wharf piles (Figure 8). It dies back in winter, reappearing in spring and vast numbers of colonies grow profusely through the summer. It is abundant in the lower intertidal and subtidal parts of the proposed marina footprint, on pilings and mooring blocks and natural sandstone outcrops and open sand bottom in the channel (Figures 9 to 15).

It is a biosecurity risk for aquaculture, particularly oyster farms, but surprisingly it has not yet been given “unwanted organism” status, perhaps because it is assumed it will not move south of 37 degrees latitude because of its warmer water preferences. It was historically found at Tauranga and Picton but may have died out at those sites because of lower water temperatures. It has also been assumed that it has an “apparent preference for artificial substrates in the intertidal zone, making it readily accessible for manual clearance” (Smith et.al. 2007). Obviously this is not the case, as at Sandspit it is abundant on natural sandstone and other substrates in the subtidal channel and would be impossible to clear manually.

The ability of the Australian droplet tunicate to spread naturally is severely limited by its very short pelagic larval life of less than 24 hours. This may have contributed to the fact that it has not yet been seen in the Whangateau Harbour, the next small estuary to the north. The major vectors in its further spread are human activities such as boating movements and transport of aquaculture gear. At Sandspit a huge imminent risk of spreading it to areas where it is currently not found is the proposal to dredge a marina basin, requiring the removal of thousands of tons of sandstone rock and sediment presently covered in literally millions of colonies of the droplet tunicate, to be dumped………where? East of Great Barrier? Sandspit is apparently presently the southernmost occurrence of the Australian droplet tunicate. Dumping dredgings from the marina anywhere further south or east would risk a significant range extension of this highly invasive species.

Although having no formal biosecurity status, the Australian droplet tunicate is recognized as a threat as it is an “unsightly invasive marine organism in the native coastal environment. It is also a significant nuisance to marine farming.”(Biosecurity NZ, 2007). I believe the Australian droplet tunicate is a serious biosecurity concern.

Figure 8. The Australian droplet tunicate is seasonally abundant on the Sandspit wharf. Here photographed in January 2011.

Figure 9. These small colonies of Eudistoma elongatum at Rainbow’s End in early January 2014 are rapidly growing and will be much larger toward the end of summer.

Figure 10. The GPS reading (36°23.392’S;174°43.605’E) puts this colony of Australian droplet tunicates near the northern edge of the proposed marina.

Figure 11. These droplet tunicates are clearly within the proposed marina footprint and would be carried with the dredgings to the dump site.

Figure 12. This infestation of Australian droplet tunicate on the sandstone edge of the channel near the northern end of the proposed marina, is just a small sample of millions of colonies in the marina footprint which will potentially be dredged and dumped offshore, perhaps to infest other shores..

Figure 13. On the channel floor in the marina footprint “sea snot” is abundant on mooring blocks but also on the natural seabed of shelly sand.

Figure 15. “Sea snot” growing on other encrusting life on Lee’s jetty piles.

6. Biosecurity risk for marina development plans

6.1. Biosecurity Management Plan

Although the marina developers have their consents in place, there are conditions they are required to comply with as detailed in their Marina Structures and Dredging Permit 41065. Under Condition Number 23 Biosecurity they are required to lodge a Biosecurity Management Plan with the Manager. The conditions address the potential for the introduction of unwanted or risk species to the Sandspit estuary via vessels and equipment brought to Sandspit for the construction of the marina.

Unfortunately there appears to be no consideration for the potential to spread unwanted or risk species from Sandspit to other areas. The objectives of the Plan are listed in Section 23.3, which includes clause iv) To ensure effective treatment of all the equipment used in association with the marina construction to ensure it does not become a vector for the spread of any unwanted or risk species, including but not limited to Undaria. The intention in that clause is clear, in that there should be no spread of unwanted or risk species, but the wording is such that it deals only with the concept of introducing organisms to Sandspit, not exporting them.

There may be an opportunity in clause 23.4 to address this apparent oversight: 23.4 The Biosecurity Management Plan shall be reviewed annually by the Consent Holder for the purpose of determining whether the terms are adequate to meet the objectives set out in condition 23.3, having regard to any change in circumstances. Any amendments to the Biosecurity Management Plan shall be approved by the Manager.

Perhaps a review of the Biosecurity Management Plan can be instigated in view of the changing circumstances, that is the discovery of an “unwanted organism” (clubbed tunicate) and the abundance of a risk species (Australian droplet tunicate) in the proposed marina footprint, neither of which should be spread via dumping of dredge spoil?

6.2. Dumping Permit

Alternatively there may be an opportunity in the dredge spoil dumping permit to address the issue of spreading harmful species. My understanding is that the biosecurity risk associated with dumping is handled by the consent authority who grants approval to the company doing the dumping. Clause 1a of Coastal Resource’s permit granted by Maritime New Zealand (MNZ) for the dump site east of Great Barrier Island states:

“Before any collection occurs from a Source Site, the Permit Holder must complete pre-disposal sampling of sediments for dredging. All pre-disposal sampling must include physical nature, contaminants and biosecurity threats. The Permit Holder must submit the Sampling Results to the Director for approval, before removal of sediment for disposal is permitted. The Sampling Results must include comment regarding biosecurity threats from Biosecurity New Zealand (or its successor)”

Apparently Maritime New Zealand does not, after 28 June 2013, handle disposal of waste at sea permits. This function is now carried out by the Environmental Protection Agency (EPA), and as of October 2013 they had not processed any applications. If an application has been received since then, I would seek assurance that the main “risk” species identified in this report have been adequately addressed through the EPA process.

6.3. NZ Coastal Policy Statement

The New Zealand Coastal Policy Statement 2010 has a section on Harmful aquatic organisms in Policy 12 which states:

(1) Provide in regional policy statements and in plans, as far as practicable, for the control of activities in or near the coastal marine area that could have adverse effects on the coastal environment by causing harmful aquatic organisms to be released or otherwise spread, and include conditions in resource consents, where relevant, to assist with managing the risk of such effects occurring. (2) Recognise that activities relevant to (1) include: (b) the discharge or disposal of organic material from dredging, or from vessels or structures, whether during maintenance, cleaning or otherwise; and whether in the coastal marine area or on land.

Harmful aquatic organisms are defined as:

“Aquatic organisms which, if introduced into coastal water, may adversely affect the environment or biological diversity, pose a threat to human health, or interfere with legitimate use or protection of natural and physical resources in the coastal environment.”

Clearly the main three “problem” species at Sandspit, that is clubbed tunicate, Australian droplet tunicate, and Asian paddle crab, fit within the definition of “harmful aquatic organisms” above, and therefore could come under the influence of the NZCPS Policy 12.

My understanding, however, is that the dumping is to take place beyond the territorial sea (12 nautical miles offshore) and therefore would not come under influence of the NZCPS which stops within the territorial sea. The problem with release of harmful aquatic organisms just beyond the territorial sea is that they, or their propagules, could drift back into the territorial sea and indeed into inshore coastal waters where they may establish viable colonies. This should be avoided and the NZCPS may thus have some influence over the dumping activity by anticipating a shoreward effect from the dumping.

7. Conclusions

1. There are three invasive marine species in the Sandspit estuary which are undesirable inhabitants. All are present in the proposed marina footprint. It would be unwise, and in one case illegal, to knowingly move these species to other areas where they may not currently be present.

2. The Asian paddle crab is very aggressive and has the potential to change the shallow reef ecosystem by competing with native species and altering the trophic balance. It may also become a nuisance to swimmers.

3. The clubbed tunicate is officially classed as an “unwanted organism” and it is illegal to knowingly move it to other marine areas without specific approval from the relevant authorities.

4. The Australian droplet tunicate, colloquially known as “sea snot”, is abundant in the Sandspit estuary and the proposed marina footprint. It smothers other marine life and is an unsightly undesirable organism in the estuary. Sandspit is the southernmost record in its present known range.

5. Dredged sandstone and sediments from the proposed marina site will inevitably contain these three species, and especially millions of colonies of the Australian droplet tunicate. The dumping of this material at sea is likely to spread these species to other areas where they are probably not present.

6. All legal means to prevent further spread of these three undesirable species should be pursued.

Smith, P.J., Page, M., Handley, S.J., McVeagh, S.M., and Ekins, M. 2007 First record of the Australian ascidian Eudistoma elongatum in northern New Zealand. NZ Journal of Marine and Freshwater Research 41:347-355.